Hybrid drill bit

ABSTRACT

A method for optimizing drill bit design and several embodiments of an optimized drill bit for drilling a well in an earth formation. In one embodiment, the optimized drill bit comprises a diamond impregnated bit body with one or more cutting elements, the cutting element comprising a cutting table and a substrate. The substrate preferably comprises a material that will support the cutting table during normal drilling operations and wear when exposed to the earth formation, thereby limiting the effects of wear flat areas on drilling efficiency. Alternatively, or additionally, the cutting elements may be placed, or spaced, so as to limiting the effects of wear flat areas on drilling efficiency.

CROSS REFERENCE TO RELATED APPLICATIONS

This subject matter of this application is similar to the subject matterdisclosed in U.S. patent application Ser. Nos. 12/250,443, 12/250,445,12/250,447, and 12/250,448, all filed Oct. 13, 2008, which areincorporated herein by specific reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The inventions disclosed and taught herein relate generally to drillbits for drilling wells; and more specifically relate to diamondimpregnated drill bits with super-abrasive cutting elements for drillingwells in earth formations.

2. Description of the Related Art

U.S. Pat. No. 6,095,265 discloses “a diamond impregnated bit with anadaptive matrix in the ribs. The ribs have at least two different areasof metal-matrix composite impregnated with diamonds with different wearresistance such that during boring of formation, the areas will wear atdifferent rates and provide fluid flow spaces across the surface of theribs.”

U.S. Pat. No. 6,296,069 discloses a “drill bit as used in particular inthe oil well drilling field comprising a central body (2), cuttingblades (3) protruding with respect to the body (2), both at the front ofthis body according to a drill direction and at the sides of this samebody (2), and cutting elements (9) divided over an outer front surface(10) and over an outer lateral well sizing surface (11) comprised byeach blade (3), wherein there are provided as cutting elements: in acentral area (13) of the front surface (10), on at least one blade (3):at least one synthetic polycrystalline diamond compact cutting disc(12), and in a remaining area (14) of the front surface (10) of thisblade, situated beyond said central area (13) with respect to therotation axis, and on the other blades: thermally stable syntheticdiamonds and/or impregnated diamond particles.”

U.S. Pat. No. 6,510,906 discloses a “drill bit employing a plurality ofdiscrete, post-like diamond grit impregnated cutting structuresextending upwardly from abrasive particulate-impregnated blades defininga plurality of fluid passages therebetween on the bit face. PDC cutterswith faces oriented in the general direction of bit rotation are placedin the cone of the bit, which is relatively shallow, to promote enhanceddrilling efficiency through softer, non-abrasive formations. A pluralityof ports, configured to receive nozzles therein are employed forimproved drilling fluid flow and distribution. The blades may extendradially in a linear fashion, or be curved and spiral outwardly to thegage to provide increased blade length and enhanced cutting structureredundancy.”

U.S. Pat. No. 6,843,333 discloses a “drill bit employing a plurality ofdiscrete, post-like, abrasive, particulate-impregnated cuttingstructures extending upwardly from abrasive, particulate-impregnatedblades defining a plurality of fluid passages therebetween on the bitface. Additional cutting elements may be placed in the cone of the bitsurrounding the centerline thereof. The blades may extend radially in alinear fashion, or be curved and spiral outwardly to the gage to provideincreased blade length and enhanced cutting structure redundancy.Additionally, discrete protrusions may extend outwardly from at leastsome of the plurality of cutting structures. The discrete protrusionsmay be formed of a thermally stable diamond product and may exhibit agenerally triangular cross-sectional geometry relative to the directionof intended bit rotation.”

The inventions disclosed and taught herein are directed to an improveddiamond impregnated drill bit with super-abrasive cutting elements fordrilling wells in earth formations.

BRIEF SUMMARY OF THE INVENTION

The invention relates to a method for optimizing drill bit design andseveral embodiments of an optimized drill bit for drilling a well in anearth formation. In one embodiment, the optimized drill bit comprises adiamond impregnated bit body with one or more cutting elements, thecutting element comprising a cutting table and a substrate. Thesubstrate preferably comprises a material that will support the cuttingtable during normal drilling operations and wear when exposed to theearth formation, thereby limiting the effects of wear flat areas ondrilling efficiency. Alternatively, or additionally, the cuttingelements may be placed, or spaced, so as to limiting the effects of wearflat areas on drilling efficiency.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 comprises an inverted perspective view of a first embodiment of abit of the present invention;

FIG. 2 is a top elevation of the bit of FIG. 1 after testing, showingwear of the discrete cutting structures and PDC cutters; and

FIG. 3 is an enlarged perspective view of an exemplary cutting elementembodying certain aspects of the present inventions.

DETAILED DESCRIPTION

The Figures described above and the written description of specificstructures and functions below are not presented to limit the scope ofwhat Applicants have invented or the scope of the appended claims.Rather, the Figures and written description are provided to teach anyperson skilled in the art to make and use the inventions for whichpatent protection is sought. Those skilled in the art will appreciatethat not all features of a commercial embodiment of the inventions aredescribed or shown for the sake of clarity and understanding. Persons ofskill in this art will also appreciate that the development of an actualcommercial embodiment incorporating aspects of the present inventionswill require numerous implementation-specific decisions to achieve thedeveloper's ultimate goal for the commercial embodiment. Suchimplementation-specific decisions may include, and likely are notlimited to, compliance with system-related, business-related,government-related and other constraints, which may vary by specificimplementation, location and from time to time. While a developer'sefforts might be complex and time-consuming in an absolute sense, suchefforts would be, nevertheless, a routine undertaking for those of skillthis art having benefit of this disclosure. It must be understood thatthe inventions disclosed and taught herein are susceptible to numerousand various modifications and alternative forms. Lastly, the use of asingular term, such as, but not limited to, “a,” is not intended aslimiting of the number of items. Also, the use of relational terms, suchas, but not limited to, “top,” “bottom,” “left,” “right,” “upper,”“lower,” “down,” “up,” “side,” and the like are used in the writtendescription for clarity in specific reference to the Figures and are notintended to limit the scope of the invention or the appended claims.

Particular embodiments of the invention may be described below withreference to block diagrams and/or operational illustrations of methods.In some alternate implementations, the functions/actions/structuresnoted in the figures may occur out of the order noted in the blockdiagrams and/or operational illustrations. For example, two operationsshown as occurring in succession, in fact, may be executed substantiallyconcurrently or the operations may be executed in the reverse order,depending upon the functionality/acts/structure involved.

Applicants have created both a method for optimizing drill bit designand several embodiments of an optimized drill bit for drilling a well inan earth formation. In one embodiment, the optimized drill bit comprisesa diamond impregnated bit body with one or more cutting elements, thecutting element comprising a cutting table and a substrate. Thesubstrate preferably comprises a material that will support the cuttingtable during normal drilling operations and wear when exposed to theearth formation, thereby limiting the effects of wear flat areas ondrilling efficiency. Alternatively, or additionally, the cuttingelements may be placed, or spaced, so as to limit the effects of wearflat areas on drilling efficiency.

The present invention includes both a method for optimizing drill bitdesign and several embodiments of an optimized drill bit 10 for drillinga well in an earth formation. The bit 10 may be similar to thosedisclosed in U.S. Pat. No. 6,843,333, the disclosure of which isincorporated herein by specific reference in its entirety. Referring nowto FIGS. 1 and 2, a first embodiment of the bit 10 of the presentinvention is depicted. In FIG. 1, the bit 10 is shown inverted from itsnormal face-down operating orientation for clarity. The bit 10 is, inone embodiment, 8½″ in diameter and includes a matrix-type bit body 12having a shank 14 for connection to a drill string (not shown) extendingtherefrom opposite a bit face 16. A plurality of blades 18 extendsgenerally radially outwardly in linear fashion to gage pads 20 definingjunk slots 22 therebetween.

The bit 10 may include conventional impregnated bit cutting structuresand/or discrete, impregnated cutting structures 24 comprising postsextending upwardly from the blades 18 on the bit face 16. The cuttingstructures 24 may be formed as an integral part of the matrix-typeblades 18 projecting from the matrix-type bit body 12 by hand-packingdiamond grit-impregnated matrix material in mold cavities on theinterior of a bit mold defining locations of the cutting structures 24and blades 18. Thus, each blade 18 and associated cutting structure 24may define a unitary structure. It is noted that the cutting structures24 may be placed directly on the bit face 16, dispensing with theblades. It is also noted that, while discussed in terms of beingintegrally formed with the bit 10, the cutting structures 24 may beformed as discrete individual segments, such as by hot isostaticpressing, and subsequently brazed or furnaced onto the bit 10.

The discrete cutting structures 24 may be mutually separate from eachother to promote drilling fluid flow therearound for enhanced coolingand clearing of formation material removed by the diamond grit. Thediscrete cutting structures 24 may be generally of a round or circulartransverse cross-section at their substantially flat, outermost ends,but become more oval with decreasing distance from the face of theblades 18 and thus provide wider or more elongated (in the direction ofbit rotation) bases for greater strength and durability. As the discretecutting structures 24 wear, the exposed cross-section of the postsincreases, providing progressively increasing contact area for thediamond grit with the formation material. As the cutting structures weardown, the bit 10 takes on the configuration of a heavier-set bit moreadept at penetrating harder, more abrasive formations. Even if discretecutting structures 24 wear completely away, the diamond-impregnatedblades 18 will provide some cutting action, reducing any possibility ofring-out and having to pull the bit 10.

While the cutting structures 24 are illustrated as exhibiting posts ofcircular outer ends and oval shaped bases, other geometries are alsocontemplated. For example, the outermost ends of the cutting structuresmay be configured as ovals having a major diameter and a minor diameter.The base portion adjacent the blade 18 might also be oval, having amajor and a minor diameter, wherein the base has a larger minor diameterthan the outermost end of the cutting structure 24. As the cuttingstructure 24 wears towards the blade 18, the minor diameter increases,resulting in a larger surface area. Furthermore, the ends of the cuttingstructures 24 need not be flat, but may employ sloped geometries. Inother words, the cutting structures 24 may change cross-sections atmultiple intervals, and tip geometry may be separate from the generalcross-section of the cutting structure. Other shapes or geometries maybe configured similarly. It is also noted that the spacing betweenindividual cutting structures 24, as well as the magnitude of the taperfrom the outermost ends to the blades 18, may be varied to change theoverall aggressiveness of the bit 10 or to change the rate at which thebit is transformed from a light-set bit to a heavy-set bit duringoperation. It is further contemplated that one or more of such cuttingstructures 24 may be formed to have substantially constantcross-sections if so desired depending on the anticipated application ofthe bit 10.

Discrete cutting structures 24 may comprise a synthetic diamond grit,such as, for example, DSN-47 Synthetic diamond grit, commerciallyavailable from DeBeers of Shannon, Ireland, which has demonstratedtoughness superior to natural diamond grit. The tungsten carbide matrixmaterial with which the diamond grit is mixed to form discrete cuttingstructures 24 and supporting blades 18 may desirably include a finegrain carbide, such as, for example, DM2001 powder commerciallyavailable from Kennametal Inc., of Latrobe, Pa. Such a carbide powder,when infiltrated, provides increased exposure of the diamond gritparticles in comparison to conventional matrix materials due to itsrelatively soft, abradable nature. The base 30 of each blade 18 maydesirably be formed of, for example, a more durable 121 matrix material,obtained from Firth MPD of Houston, Tex. Use of the more durablematerial in this region helps to prevent ring-out even if all of thediscrete cutting structures 24 are abraded away and the majority of eachblade 18 is worn.

It is noted, however, that alternative particulate abrasive materialsmay be suitably substituted for those discussed above. For example, thediscrete cutting structures 24 may include natural diamond grit, or acombination of synthetic and natural diamond grit. Alternatively, thecutting structures may include synthetic diamond pins. Additionally, theparticulate abrasive material may be coated with a single layer ormultiple layers of a refractory material, as known in the art anddisclosed in U.S. Pat. Nos. 4,943,488 and 5,049,164, the disclosures ofeach of which are hereby incorporated herein by reference in theirentirety. Such refractory materials may include, for example, arefractory metal, a refractory metal carbide or a refractory metaloxide. In one embodiment, the coating may exhibit a thickness ofapproximately 1 to 10 microns. In another embodiment, the coating mayexhibit a thickness of approximately 2 to 6 microns. In yet anotherembodiment, the coating may exhibit a thickness of less than 1 micron.

In one embodiment, one or more of the blades 18 carry cutting elements,shown as polycrystalline diamond compact (PDC) cutters 26, inconventional orientations, with cutting faces oriented generally facingthe direction of bit rotation. In one embodiment, the PDC cutters 26 arelocated within the cone portion 34 of the bit face 16. The cone portion34, best viewed with reference to FIG. 1, is the portion of the bit face16 wherein the profile is defined as a generally cone-shaped sectionabout the centerline of intended rotation of the drill bit 10.Alternatively, or additionally, the PDC cutters 26 may be located acrossthe blades 18 and elsewhere on the bit 10.

The PDC cutters 26 may comprise cutters having a PDC jacket or sheathextending contiguously with, and to the rear of, the PDC cutting faceand over a supporting substrate 32. For example, a cutter of this typeis offered by Hughes Christensen Company, a wholly owned subsidiary ofthe assignee of the present invention, as NIAGARA™ cutters. Such cuttersare further described in U.S. Pat. No. 6,401,844, the disclosure ofwhich is incorporated herein by specific reference in its entirety. Thiscutter design provides enhanced abrasion resistance to the hard and/orabrasive formations typically drilled by impregnated bits, incombination with enhanced performance, or rate of penetration (ROP), insofter, nonabrasive formation layers interbedded with such hardformations. It is noted, however, that alternative PDC cutter designsmay be implemented. For example, the PDC cutters 26 may be configured ofvarious shapes, sizes, or materials as known by those of skill in theart. Also, other types of cutting elements may be formed within the coneportion 34 of, and elsewhere across, the bit 10 depending on theanticipated application of the bit 10. For example, the cutting elements26 may include cutters formed of thermally stable diamond product (TSP),natural diamond material, or impregnated diamond.

An exemplary cutting element 26 of the present invention, as shown inFIG. 3, includes a super-abrasive cutting table 28 of circular,rectangular or other polygon, oval, truncated circular, triangular, orother suitable cross-section. The super-abrasive table 28, exhibiting acircular cross-section and an overall cylindrical configuration, orshape, is suitable for a wide variety of drill bits and drillingapplications. The super-abrasive table 28 of the cutting element 26 ispreferably formed with a conglomerated super-abrasive material, with anexposed cutting face 30. The cutting face 30 will typically have a top30A and a side 30B with the peripheral junction thereof serving as thecutting region of the cutting face 30 and more precisely a cutting edge30C of the cutting face 30, which is usually the first portion of thecutting face 30 to contact and thus initially “cut” the formation as thedrill bit 10 retaining the cutting element 26 progressively drills abore hole. The cutting edge 30C may be a relatively sharp approximatelyninety-degree edge, or may be beveled or rounded. The super-abrasivetable 28 will also typically have a primary underside, or attachment,interface joined during the sintering of the diamond, or super-abrasive,layer forming the super-abrasive table 28 to a supporting substrate 32typically formed of a hard and relatively tough material such as acemented tungsten carbide or other carbide. The substrate 32 may bepreformed in a desired shape such that a volume of particulate diamondmaterial may be formed into a polycrystalline cutting, orsuper-abrasive, table 28 thereon and simultaneously strongly bonded tothe substrate 32 during high pressure high temperature (HPHT) sinteringtechniques practiced within the art. Alternatively, the substrate 32 maybe formed of steel, or other strong material with an abrasion resistanceless than that of tungsten carbide and/or the earth formation beingdrilled. In still other embodiments, the substrate 32 may comprise arelatively thin tungsten carbide layer backed by a steel body.

In any case, the substrate 32 may be cylindrical, conical, tapered,and/or rectangular in over-all shape, as well as, circular, rectangularor other polygon, oval, truncated circular, and/or triangular, incross-section. A unitary cutting element 26 will thus be provided thatmay then be secured to the drill bit 10 by brazing or other techniquesknown within the art, such as gluing, press fitting, and/or using a studmounting technique.

In accordance with the present invention, the super-abrasive table 28preferably comprises a heterogeneous conglomerate type of PDC layer ordiamond matrix in which at least two different nominal sizes and wearcharacteristics of super-abrasive particles, such as diamonds ofdiffering grains, or sizes, are included to ultimately develop a rough,or rough cut, cutting face 30, particularly with respect to the cuttingface side 30B and most particularly with respect to the cutting edge30C. In one embodiment, larger diamonds may range upwards ofapproximately 600 μm, with a preferred range of approximately 100 μm toapproximately 600 μm, and smaller diamonds, or super-abrasive particles,may preferably range from about 15 μm to about 100 μm. In anotherembodiment, larger diamonds may range upwards of approximately 500 μm,with a preferred range of approximately 100 μm to approximately 250 μm,and smaller diamonds, or super-abrasive particles, may preferably rangefrom about 15 μm to about 40 μm.

The specific grit size of larger diamonds, the specific grit size ofsmaller diamonds, the thickness of the cutting face 30 of thesuper-abrasive table 28, the amount and type of sintering agent, as wellas the respective large and small diamond volume fractions, may beadjusted to optimize the cutter 26 for cutting particular formationsexhibiting particular hardness and particular abrasivenesscharacteristics. The relative, desirable particle size relationship oflarger diamonds and smaller diamonds may be characterized as a tradeoffbetween strength and cutter aggressiveness. On the one hand, thedesirability of the super-abrasive table 28 holding on to the largerparticles during drilling would dictate a relatively smaller differencein average particle size between the smaller and larger diamonds. On theother hand, the desirability of providing a rough cutting surface woulddictate a relatively larger difference in average particle size betweenthe smaller and larger diamonds. Furthermore, the immediately precedingfactors may be adjusted to optimize the cutter 26 for the averagerotational speed at which the cutting element 26 will engage theformation as well as for the magnitude of normal force and torque towhich each cutter 26 will be subjected while in service as a result ofthe rotational speeds and the amount of weight, or longitudinal force,likely to be placed on the drill bit 10 during drilling.

While PDC cutters, such as those discussed above, are used in apreferred embodiment, other cutters may be used alternatively and/oradditionally. For example, cutters made of thermally stablepolycrystalline (TSP) diamond, in triangular, pin, and/or circularconfiguration, cubic boron nitride (CBN), and/or other superabrasivematerials may be used. In some embodiments, even simple carbide cuttersmay be used.

According to certain aspects of the present invention, rather thanconstructing every component of the drill bit 10 from the strongest,most durable and abrasion resistant materials available, it maybeneficial to make portions of the drill bit 10 sacrificial. Forexample, with drilling rig day rates often significantly exceeding thecost of drill bits, designing a drill bit that minimizes the cost ofdrilling operations is paramount. Historically, drill bits have beendesigned to be as durable and wear resistant as possible. Unfortunately,due to the extreme environment in which they are expected to perform,all known drill bits experience wear. More specifically, as the drillbit 10 wears, wear flat areas develop on the bit body 12, blades 18, andthe cutters 26 themselves. These wear flat areas abrade against theearth formation, such as rock, and cause unproductive heat, drag, aswell as other harmful byproducts of the drilling operation. The heat anddrag further degrade the drill bit 10 and increase the wear flatproblem, requiring more and more energy as well as decreasing rate ofpenetration. More specifically, increased wear flat area increases thespecific energy, or the energy required to remove a unit volume of rock.At some point, the wear flat area becomes so great that the specificenergy required is too great, drilling efficiency is therefore lost, andthe drill bit 10 must be replaced.

Clearly, the cutting tables 28 must be made from a material with anabrasion resistance greater than the abrasiveness of the earthformation, in order to cut therethrough. Because the substrate 32 isintended to provide support to the cutting table 28, rather thansignificantly contribute to the rate of penetration, the substrate 32may be made of a material with an abrasion resistance less than theabrasiveness of the earth formation. Therefore, in some embodiments, thesubstrates 32 of the cutting elements 26 and/or other portions of thebit body 12 are preferably made of a material with less abrasionresistance than that of the cutting table 28 and/or the earth formationinto which the drill bit 10 is drilling. In one embodiment, cutters 26with sacrificial substrates 32 could be mounted on every blade 18,spaced SO as to minimize the wear flat area's influence on the requiredspecific energy. The wear flat area's influence may also be minimized bymounting cutters 26 with sacrificial substrates 32 on every other blade18.

The above differences in abrasiveness can be accomplished in terms ofindependently specified material properties. For example, the optimizeddrill bit 10 according to the present invention may be designed suchthat the cutting table 28 is made of a cutting material with a minimumabrasion resistance, significantly higher than the abrasiveness of theearth formation. The optimized drill bit 10 according to the presentinvention may be designed such that the substrate 32 is made of asubstrate material with a minimum and/or maximum abrasion resistance,which is preferably lower than the abrasiveness of the earth formation.

Alternatively, the above differences in abrasiveness can be accomplishedin terms of specified ratios. For example, an optimized drill bit 10according to the present invention may be designed to maintain a minimumratio of abrasion resistance between: the cutting table 28 and the earthformation; the cutting table 28 and the substrate 32; and/or earthformation and the substrate 32. In any case, as discussed above, theabrasiveness of the earth formation is preferably such that at least thesubstrate material erodes rather quickly when and where it comes intofrictional contact with the earth formation.

It can be appreciated that a pre-designed and pre-manufactured drill bitmay be selected based on the earth formation predicted and/orencountered. Alternatively, a drill bit may be specifically designed forthe earth formation predicted and/or encountered.

It has been discovered that the blades 18 rarely wear evenly. Therefore,it may be desirable to optimize the design of the blades 18 and thedistribution and/or spacing of cutting material along the blades 18, toincrease drill bit useful life and minimize the required specific energywhile maintaining an acceptable rate of penetration and drillingefficiency. The blades 18 of modern drill bits often have three or moresections that serve related and overlapping functions. Specifically,each blade 18 preferably has a cone section, a nose section, a shouldersection, and a gage section.

As discussed above, the cone section of each blade is preferably asubstantially linear section extending from near a center-line of thedrill bit 10 outward. Because the cone section is nearest thecenter-line of the drill bit 10, the cone section does not experience asmuch, or as fast, movement relative to the earth formation. Therefore,it has been discovered that the cone section commonly experiences lesswear than the other sections. Thus, the cone section can maintaineffective and efficient rate of penetration with less cutting material.This can be accomplished in a number of ways. For example, the conesection may have fewer cutting structures 24 and/or PDC cutters 26,smaller cutting structures 24 and/or PDC cutters 26, and/or more spacingbetween cutting structures 24 and/or PDC cutters 26. The cone angle fora PDC bit is typically 15-25°, although, in some embodiments, the conesection is essentially flat, with a substantially 0° cone angle.

The nose represents the lowest point on a drill bit. Therefore, the nosecutter is typically the leading most cutter. The nose section is roughlydefined by a nose radius. A larger nose radius provides more area toplace cutters in the nose section. The nose section begins where thecone section ends, where the curvature of the blade begins, and extendsto the shoulder section. More specifically, the nose section extendswhere the blade profile substantially matches a circle formed by thenose radius. The nose section experiences much more, and more rapid,relative movement than does the cone section. Additionally, the nosesection typically takes more weight than the other sections. As such,the nose section commonly experiences much more wear than does the conesection. Therefore, the nose section preferably has a higherdistribution, concentration, or density of cutting structures 24 and/orPDC cutters 26.

The shoulder section begins where the blade profile departs from thenose radius and continues outwardly on each blade 18 to a point where aslope of the blade is essentially completely vertical, at the gagesection. The shoulder section experiences much more, and more rapid,relative movement than does the cone section. Additionally, the shouldersection typically takes the brunt of abuse from dynamic dysfunction,such as bit whirl. As such, the shoulder section experiences much morewear than does the cone section. The shoulder section is also a moresignificant contributor to rate of penetration and drilling efficiencythan the cone section. Therefore, the shoulder section preferably has ahigher distribution, concentration, or density of cutting structures 24and/or PDC cutters 26. Depending on application, the nose section or theshoulder section may experience the most wear, and therefore either thenose section or the shoulder section may have the highest distribution,concentration, or density of cutting structures 24 and/or PDC cutters26.

The gage section begins where the shoulder section ends. Morespecifically, the gage section begins where the slope of the blade ispredominantly vertical. The gage section continues outwardly to an outerperimeter or gauge of the drill bit 10. The gage section experiences themost, and most rapid, relative movement with respect to the earthformation. However, at least partially because of the high,substantially vertical, slope of the blade 18 in the gage section, thegage section does not typically experience as much wear as does theshoulder section and/or the nose section. The gage section does,however, typically experience more wear than the cone section.Therefore, the gage section preferably has a higher distribution ofcutting structures 24 and/or PDC cutters 26 than the cone section, butmay have a lower distribution of cutting structures 24 and/or PDCcutters 26 than the shoulder section and/or nose section.

In one embodiment, a highest concentration of the cutting structures 24and/or PDC cutters 26 occurs near the border between the shouldersection and the gage section. Alternative embodiments may include ahighest concentration of the cutting structures 24 and/or PDC cutters26, in the shoulder section and/or the gage section.

Upon reading this disclosure, it can be appreciated that the design of adrill bit includes consideration of many factors, such as the size,shape, spacing, orientation, and number of blades; the size, shape,spacing, orientation, and number of cutters, or cutting elements; aswell as the materials of the bit body, blades, cutting tables, andsubstrates. All of these factors may be considered in light of thematerials of the earth formation(s) for which the drill bit is designedand/or matched.

The bit 10 may employ a plurality of ports 36 over the bit face 16 toenhance fluid velocity of drilling fluid flow and better apportion theflow over the bit face 16 and among fluid passages 38 between blades 18and extending to junk slots 22. This enhanced fluid velocity andapportionment helps prevent bit balling in shale formations, forexample, which phenomenon is known to significantly retard rate ofpenetration (ROP). Further, in combination with the enhanced diamondexposure of bit 10, the improved hydraulics substantially enhancesdrilling through permeable sandstones.

Other and further embodiments utilizing one or more aspects of theinventions described above can be devised without departing from thespirit of Applicant's invention. For example, the various methods andembodiments of the drill bit 10 can be included in combination with eachother to produce variations of the disclosed methods and embodiments.Reading this disclosure, it can be appreciated that there are a numberof ways to impact concentrations or distributions of cutter volume, suchas by using differently sized, shaped, and/or spaced cutters. Discussionof singular elements can include plural elements and vice-versa.

The order of steps can occur in a variety of sequences unless otherwisespecifically limited. The various steps described herein can be combinedwith other steps, interlineated with the stated steps, and/or split intomultiple steps. Similarly, elements have been described functionally andcan be embodied as separate components or can be combined intocomponents having multiple functions.

The inventions have been described in the context of preferred and otherembodiments and not every embodiment of the invention has beendescribed. Obvious modifications and alterations to the describedembodiments are available to those of ordinary skill in the art. Thedisclosed and undisclosed embodiments are not intended to limit orrestrict the scope or applicability of the invention conceived of by theApplicants, but rather, in conformity with the patent laws, Applicantsintend to fully protect all such modifications and improvements thatcome within the scope or range of equivalent of the following claims.

1. A method of designing a drill bit, such as for drilling into an earthformation, the method comprising the steps of: configuring the drill bitwith a diamond impregnated bit body and at least one cutting element,the cutting element comprising a cutting table and a substrate; andselecting a material for the substrate so that the substrate willsupport the cutting table during normal drilling operations and wearwhen exposed to the earth formation, thereby limiting the effects ofwear flat areas on drilling efficiency.
 2. The method as set forth inclaim 1, wherein the cutting table is operable to cut the earthformation.
 3. The method as set forth in claim 1, wherein the bit bodyis operable to cut the earth formation.
 4. The method as set forth inclaim 1, wherein the cutting table has an abrasion resistance greaterthan the earth formation.
 5. The method as set forth in claim 1, whereinthe bit body has an abrasion resistance greater than the earthformation.
 6. The method as set forth in claim 1, wherein the substratehas an abrasion resistance less than the earth formation.
 7. The methodas set forth in claim 1, wherein the substrate has an abrasionresistance less than the cutting table.
 8. The method as set forth inclaim 1, wherein the substrate has an abrasion resistance less than thebit body.
 9. The method as set forth in claim 1, further including thestep of arranging a plurality of diamond impregnated cutting structureson the bit body.
 10. The method as set forth in claim 1, furtherincluding the step of arranging a plurality of diamond impregnatedcutting structures among the cutting elements.
 11. A method of designinga drill bit, such as for drilling into an earth formation, the methodcomprising the steps of: configuring the drill bit with a diamondimpregnated bit body and a plurality of cutting elements, the cuttingelement comprising a cutting table and a substrate; and placing thecutting elements on the bit body to limit the effects of wear flat areason drilling efficiency.
 12. The method as set forth in claim 11, whereinthe cutting elements are spaced tighter in a shoulder section of the bitbody.
 13. The method as set forth in claim 11, wherein the cuttingelements are spaced tighter in a nose section of the bit body.
 14. Themethod as set forth in claim 11, wherein the cutting elements havegreater spacing in a cone section of the bit body.
 15. The method as setforth in claim 11, wherein the cutting elements have greater spacing ina gage section of the bit body.
 16. The method as set forth in claim 11,further including the step of arranging a plurality of diamondimpregnated cutting structures on the bit body.
 17. The method as setforth in claim 11, further including the step of arranging a pluralityof diamond impregnated cutting structures among the cutting elements.18. A method of designing a drill bit, such as for drilling into anearth formation, the method comprising the steps of: configuring thedrill bit with a diamond impregnated bit body a plurality of diamondimpregnated cutting structures and a plurality of cutting elements, eachcutting elements comprising a cutting table and a substrate; selecting amaterial for the substrate so that the substrate will support thecutting table during normal drilling operations and wear when exposed tothe earth formation, thereby limiting the effects of wear flat areas ondrilling efficiency; and placing the cutting elements on the bit body tolimit the effects of wear flat areas on drilling efficiency.
 19. Themethod as set forth in claim 18, wherein both the cutting table and thebit body are operable to cut the earth formation, while the substratehas an abrasion resistance less than the cutting table, the bit body andthe earth formation.
 20. The method as set forth in claim 18, whereinthe cutting elements are spaced tighter in a shoulder section and a nosesection than in a cone section or a gage section of the bit body.